1. Field of the Invention
The present invention relates in general to a lancing device used to lance or puncture the skin and collect a small quantity of blood, and in particular to a disposable lancing device intended to be discarded after a single use.
2. Description of the Related Art
Self-collection of small quantities of blood is sometimes necessary for medical purposes. For example, for patients with diabetes, it is necessary for the patient himself to regularly collect his own blood in order to periodically check blood sugar level (Self-Monitoring of Blood Glucose: SMBG). Lancing devices have been in use for some time to enable such self-collection of blood to be carried out safely and dependably. In particular, for the purpose of preventing infection, lancing devices of disposable type designed to be discarded after a single use have been available in the past.
Such lancing devices typically include a lancet housed within a housing and urged by a spring member, and are designed to carry out the puncturing operation by extending a puncture member provided to the distal end of the lancet out from the housing. Specifically, as disclosed in U.S. Publication No. US 2007/0135828, the instrument is designed to be used by pushing an operating member with a lancet engaged within the housing, so that a spring member disposed deeper than the lancet experiences compressive deformation. When compression force of the spring member increases to such an extent as to disengage the lancet, the lancet will extend out from the housing to carry out the puncturing operation.
However, with the lancing devices of this conventional construction, it is difficult to establish compression force of the spring member that is required to disengage the lancet from the housing with sufficient accuracy. Consequently, there may be a case where, even though the spring member is not sufficiently compressed, the lancet might disengage to induce the puncturing operation, so that insufficient puncturing force causes shortage of exuded blood. There may be another case, on the contrary, where even if the operating member is firmly pushed, the lancet might fail to disengage, making it difficult to bring about the puncturing operation.
International Publication No. WO 2005/110227 and U.S. Pat. No. 5,755,733 disclose a structure in which a push operating member that induces compressive deformation of a spring member is furnished with an abutting portion for releasing engagement, and when the push operating member reaches a prescribed position the abutting portion comes into abutment against and disengage a detent piece of a lancet engaged by a housing. However, with such lancing devices, in addition to force for inducing compressive deformation of the spring member, force for deforming and disengaging the detent piece of the lancet should be exerted on the push operating member, thereby inevitably requiring large operating force.
Meanwhile, U.S. Publication No. US 2007/0225742 and U.S. Publication No. US 2005/0070945 disclose a structure in which a detent piece of a lancet engaged by a housing is designed to be pushed from the horizontal direction so as to release the engagement, thereby carrying out the extending action. However, since the detent piece of the lancet is subjected to pushing force from the horizontal direction, the center axis of the lancet may deviate to catch other components, or the lancet may be pressed against the other components to increase frictional resistance during the extending action, posing a risk of impaired movement of the lancet during the extending action.
Another structure is disclosed in U.S. Pat. No. 7,238,192, in which a lancet is rotatable in the circumferential direction with respect to a housing so that the engagement of the lancet with a seating surface formed to the inner face of the housing is adapted to be released by rotating action of the lancet. However, if the lancet is rotated by exerting rotational force, due to deformation or displacement of the lancet there is a risk of difficulty in duly ensuring release of the engagement or stability of the extending action. In particular, with the lancet urged by a spring member, it is difficult to rotate the lancet alone, posing another risk of inducing deformation of the spring member as well and providing adverse effects on its urging action.